It has long been known to use precision abrading processes to bring workpiece surfaces to a desired state of refinement or dimensional tolerance. This is done commonly by using a process known as lapping which removes small, controlled amounts of material with a fine abrasive grit rubbed about it in a random manner. Generally, a loose unbonded grit is employed and is mixed with a vehicle such as oil, grease, or soap and water compound. Although some lapping or finishing is done by hand, most production work is done on a lapping or finishing machine. Hence, it is desirable to employ highly effective lapping and finishing machines for precisely machining these workpiece surfaces to within relatively diminutive dimensional tolerances, which today are within microns. The concerns discussed herein are made referencing lapping machines, but also apply to finishing and polishing machines.
Many lapping machines today employ a fixed bridge supported by dual columns. The fixed bridge supports an tipper lap plate for rotation and for vertical movement between a lower lapping position and an upper position for loading and unloading the machine. The distance between these positions is known to be in some instances as much as 14 inches or more in order to load and unload workpiece carriers into the machine. This requires the upper lap plate shaft to be extended as much to set the upper lap plate at its lower lapping position. One known disadvantage to having such long shaft extension is the loss of rigidity and control during the lapping cycle, which in turn results in loss of sizing accuracy. Thus, it is desirable to eliminate such an extension for greater control during the lapping cycle.
Another known disadvantage pertains to the application of pressure during the lapping cycle. Many fixed bridge designs commonly use only a single cylinder to apply pressure from above through the upper lap plate to the lapping cycle. These single cylinder designs tend not to apply sufficient pressure for certain lapping processes.
One known solution in attempting to solve the disadvantages with extending the upper lap plate shaft down such distances includes having the lower lap plate also extend upward to meet the descending upper lap plate. That is, both the upper and lower lap plates move towards one another. Associated with this design are concerns pertaining to sealing gaskets, and the like, for the lower lap plate shaft, and hence the tendency for the abrasive fluid of the lower lap plate to flow downward and damage structure and components, such as bearing assemblies, located below. Also with dual moving lap plates, another known disadvantage is the creation of undesirable budding effects in the system during the lapping cycle.
Other lapping machines use a sliding spindle principle, but are mounted on a single column. These machines eliminate the long extension of the upper lap plate shaft. An example of one such machine is disclosed in U.S. Pat. No. 4,315.383, issued to Lawrence Day on Feb. 16, 1982. Day discloses a machine in which the upper lap plate is associated with an arm which is supported for vertical movement by the single column. To move into the lapping position, the entire arm moves downward to position the upper lap plate, and thereby eliminates the long shaft extension. This design is highly effective for precision lapping to remove an extremely small amount of material, especially when the requisite pressure to perform the particular lapping cycle is not relatively large.
One known shortcoming with the single column design is the generation of a cantilever effect during the lapping cycle. That is, when pressure is exerted during the lapping cycle, the arm and the column tend to act as a cantilever which results in loss of rigidity and control. Hence, sizing accuracy is reduced. Thus, it is desirable to eliminate this cantilevering effect.
Other known problems associated with lapping machines pertains to their cooling system designs. Some lapping machines employ cooling chambers located under the lower lapping plate to provide cooling fluid directly thereto during the lapping cycle. A disadvantage with this design is that the lapping plates by design tend to be sensitive, precision components, and thereby may become distorted by the fluid under high pressure. In performing precision machining such as this, it is critical that the temperature of the lap plates be controlled while also maintaining a substantially planar configuration for the lapping surfaces.
Other lapping machines employ copper coil systems mounted beneath the lower lap plate to control plate temperature during the lapping cycle. An advantage of the copper coil system is that it allows high pressure coolant to go through the system for faster cooling without distorting plate flatness. However, one known shortcoming of present coil designs is the tendency to have non-uniform cooling distribution. That is, the fluid is generally supplied to the coil system at the center of the lapping plate first, and as it proceeds outward through the coil, it warms up due to heat exchange with the lap plate. Consequently, the center regions of the lap plates tend to be colder than the outer regions. Experience reveals that this is especially the case with relatively large lap plates. Thus, it is desirable to have an overall cooling system which includes a more uniform cooling distribution over the lap plates.
Other known disadvantages of lapping machines pertain to distribution of the abrasive slurry used to remove material from the workpieces. Precision lapping and finishing requires optimally that the abrasive slurry be distributed uniformly over the lapping surfaces. This facilitates uniform material removal from the workpieces. However, with nonuniform distribution, the lapping cycle tends to work on the workpieces asymmetrically which results with nonconforming products. Thus, it is desirable to provide an abrasive slurry system which distributes uniformly the abrasive slurry over the lapping surfaces to ensure precise results.
It is the primary object of the present invention to provide a machine with a design that incorporates a low silhouette during the lapping or finishing cycle to facilitate greater rigidity, control and sizing accuracy.
It is another object of the present invention to provide an improved overall cooling system for lapping and finishing machines.
It is a further object of the present invention to provide an improved abrasive slurry distribution system for lapping and finishing machines.
An overall object of the present invention is to provide a lapping or finishing machine having all tile above-mentioned objects to give a complete machine which is highly durable, efficient and cost effective to manufacture, install and operate.